L4D map update

Map layout is now complete and has now entered Alpha stage. Following done:

- Geometry layout is complete.
- Textures are complete.
- Basic props are now added.
- Player start, weapon spawns, med kits are now added.
- Info director is now added. This is required for the Source engine to run the Director A.I.
- Skybox is complete. The outside brush box to display the outside environment sky.
- Cubical desks are now in place around the call center.
- Elevator room is now complete.
- Lighting is now added around the map.

To do list:

- Adjust lighting to make the map feel more of a survival-horror scenario.
- Finish placing all decals.
- Add mechanics for the elevator to be player controled.
- Finish adding more props. (computers, dead bodies, more blood, trash, etc)
- Add NAV markers.
- Begin actual gameplay testing, correct bugs, and polish.